The invention relates to a detection device of the electrical condition of a safety line extending along an aerial ropeway transport installation.
The essential role of a detection device of the kind mentioned or of a safety system for example such as described in U.S. Pat. No. 4,003,314 is to monitor the safety line and to give an installation shutdown order as soon as continuity of the line is no longer established. Interruption of the safety line may result from an end-of-travel or emergency contact opening or from the action of an incident detector, for example detecting that the rope has been derailed from the sheaves of a tower, causing a safety strip to break or the line to be cut. The break is more or less clean and the conventional devices measure the apparent resistance of the line which comprises two parameters:
the serial resistance RL, constituted by the resistance of the rope and the sum of the resistances of the contacts inserted in the line and the parallel resistance RP, due to resistive or capacitive leaks, for example at the level of the towers. Measuring the apparent resistance does not constitute a reliable method, as an incident causing an increase in the serial resistance by opening of a contact could easily be masked by a concomitant decrease in the parallel resistance, the combination of these effects being expressed by a correct apparent resistance.
The object of the present invention is to produce a reliable device which detects a safety line malfunction without any ambiguity.